Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
  • C22B11/00—Obtaining noble metals
  • C22B11/04—Obtaining noble metals by wet processes

Definitions

• the present invention relates to a process for recovery of gold from gold bearing materials and, more particularly, to a process for reclaiming gold from gold plated scrap materials by dissolving the gold in an iodide-iodine solution, precipitating gold from the solution, removing the gold and then regenerating the iodide-iodine solution by oxidation of the filtrate.
• the cyanide ion forms such a stable complex with aurous gold that when the cyanide ion is present oxygen of the air is sufficient to oxidize gold.
• the effectiveness of the cyanide process has led to its commercial usage for both extraction of gold from its ores and for the reclamation of gold from gold coated scrap parts.
• a potassium cyanide solution is used in the "cyanide process". This solution is very toxic and disposing of spent cyanide solution has become a significant and increasing waste disposal and pollution abatement control problem.
• Gold has also been dissolved using a mixture of hydrochloric acid and nitric acid, known as "aqua regia", in order to obtain the complex chlorauric acid, HAuCl 4 .
• Aqua regia is extremely corrosive and yields toxic fumes.
• a new process has now been developed. While not limited solely to reclamation type operations, the new process is particularly effective in recovering gold from parts and devices used in the electronics industry including gold plated printed circuit boards and other gold coated metal, plastic, glass and ceramic parts. Such parts may contain between 2 and 100 micro inches of plated gold.
• the new process involves the use of a potassium iodide-iodine solution to dissolve the gold. While such a solution has been used to etch out thin film gold circuits in microelectronic devices and to strip plated gold for thickness measurements, potassium iodide-iodine solutions have heretofore been considered too expensive for consideration in any commercial operation for recovering gold.
• An object of the present invention is to provide a process for the recovery of gold from gold bearing material.
• Another object of the present invention is to provide a process for the reclamation of gold from gold plated scrap materials which avoids the use of extremely corrosive and toxic materials and which accordingly avoids significant pollution problems.
• Still another object of the present invention is to provie an economical process for the reclamation of gold utilizing a potassium iodide-iodine solution.
• an aqueous iodide-iodine solution is employed to dissolve gold.
• the dissolved gold is then precipitated with a reducing solution.
• Precipitated gold can be recovered for example, by filtration.
• the iodide-iodine solution is then regenerated by oxidation of the filtrate.
• the process presents a commercially feasible gold reclamation process which is relatively safe to use and which mitigates pollution abatement problems.
• the process is particularly advantageous in recovering gold from gold plated electronic components.
• the gold is precipitated and the iodide-iodine solution is regenerated in the presence of a buffer.
• the present invention involves a process for recovering gold in an iodide-iodine water solution and then regenerating the solution.
• the process is particularly applicable to reclaiming gold from printed circuit boards and other electrical parts used in the electronic industry which have gold contacts, gold plating, gold layers, etc.
• the process of the invention utilizes iodine to oxidize the gold while iodide contributes to solubilizing the oxidized gold by formation of a gold iodide complex. Once the gold is dissolved it is then precipitated using a reducing material, the gold precipitate is filtered off and finally the iodide-iodine solution is regenerated by adding an oxidizing agent.
• Sulfur dioxide may be used as a reducing agent in an acid environment to precipitate gold from the iodide-iodine solution.
• the solution is regenerated for further gold stripping by adding a solution of hydrogen peroxide or bubbling ozone thru it.
• Hydroxylamine or hydrazine may be used as the reducing agent in an alkaline environment to precipitate gold from the iodide-iodine solution.
• the solution is then slightly acidified prior to reoxidation with hydrogen peroxide or ozone.
• Salts will build up after repeated cycles and reduce the effectiveness of the iodide-iodine stripping solution with respect to speed and capacity after repeated additions of H + and OH - ions required for the various reactions of the process.
• This build up problem is overcome in a preferred embodiment of the invention by adding a buffer to the solution which serves as a source of both H + and OH - ions.
• a buffer with pH's spanning the pH values (about 5 to about 9) at which H 2 O 2 oxidizes I 3 - and NH 2 OH reduces AuI 4 - permits the same solution to be used repeatedly without the degree of salt buildup which would otherwise occur if acid and/or alkali is employed to adjust acidity.
• Salts of weak acids and a weak base store both H + and OH - ions in solution in such a manner as to render them available to hydroxyl amine (NH 2 OH) and hydrogen peroxide (H 2 O 2 ), respectively.
• the following equation shows the conversion of dibasic ammonium phosphate to ammonium hydroxide and monobasic ammonium phosphate in the presence of water, thereby serving as a source of both H + and OH - ions.
• Iodine, I 2 in an aqueous solution of potassium iodide, KI, is present as the tri-iodide anion:
• Au gold hydroxide
• Au(OH) 3 gold hydroxide
• auric oxide Au 2 O 3
• gold recovered by the present process has a purity of 99.99%. Higher purity gold can be recovered by repeating the process. Elemental iodine regeneration also occurs with the addition of an oxidizing agent such as hydrogen peroxide:
• a buffer is preferably used during the process.
• a buffer such as dibasic ammonium phosphate in the presence of water provides OH - ions in the form of ammonium hydroxide and H + ions in the form of monobasic ammonium phosphate.
• Stainless steel, type 18-8 is one example of a suitable container material although other materials such as enameled steel, polyethylene, polypropylene, polyvinyl chloride and the like can be used.
• an agitator or tumbler is used during the stripping reaction.
• the agitator or tumbler can be made of stainless steel, a non-metallic material such as enameled steel, a plastic, or a plastic lined material. During precipitation of the gold from a gold rich solution little or no agitation is required.
• Any suitable means can be used to remove the precipitated gold. Settling and decanting, filtering the solution through a filter press or centrifuging are convenient procedures for such removal.
• the speed of the process can be increased by either heating the stripping solution or applying an electromotive force to the solution, using the material to be deplated as an anode.
• While a preferred stripping solution is made up on a weight basis of 1 part iodine, 4 parts potassium iodide and 10 parts of water these proportions are not critical.
• Aqueous solutions ranging from 1:0.7 to 1:20, on a weight basis, of iodine to potassium iodide can be used.
• a 1:4:10 (iodine to potassium iodide to water) stripping solution removed 1 microinch per minute whereas a 1:0.7:10 (iodine to potassium iodide to water) stripping solution required 5 minutes to remove the 2 microinches of gold plating.
• an effective stripping solution may be prepared by adding to elemental iodine an aqueous solution of any soluble iodine compound that yields iodide anion and a cation that is inert with respect to the chemical reactions of the processing steps.
• soluble iodine compound that yields iodide anion and a cation that is inert with respect to the chemical reactions of the processing steps.
• Specific examples include sodium iodide, calcium iodide and the like.
• reducing agents can be employed in place of hydroxylamine.
• any compound with a half cell potential that is reducing with respect to AuI 2 - and AuI 4 - in the chemical environment of the stripping solution may be used.
• Such reducing agents include hydrazine; sodium thiosulfate; sodium hydrosulfite; sodium meta bisulfite; sodium hypophosphite; sodium boro-hydride; sulfur dioxide and the like.
• Hydroxylamine can be prepared by neutralizing hydroxyl amine hydrochloride or sulfate with an alkali, such as potassium hydroxide or sodium hydroxide.
• Iodide-iodine solution regeneration is preferably accomplished by (a) decreasing the pH of the solution to below 7 after precipitation of the gold and (b) adding a chemical compound with a half cell potential which is oxidizing with respect to iodine in the solution.
• suitable buffers which can be used include any material which can supply both H + and OH - ions in the approximate pH range of between 5 and 9 and preferably between 6 and 8. Specific examples include dibasic potassium hydrogenphosphate (K 2 HPO 4 ), ammonium acetate (NH 4 C 2 H 3 O 2 ), potassium acetate (KC 2 H 3 O 2 ), sodium acetate (NaC 2 H 3 O 2 ), potassium citrate (K 3 C 6 H 5 O 7 ), sodium citrate (Na 3 C 6 H 5 O 7 ) and a solution of ammonium chloride (NH 4 Cl) and ammonium hydroxide (NH 4 OH).
• K 2 HPO 4 dibasic potassium hydrogenphosphate
• NH 4 C 2 H 3 O 2 ammonium acetate
• potassium acetate KC 2 H 3 O 2
• sodium acetate NaC 2 H 3 O 2
• potassium citrate K 3 C 6 H 5 O 7
• sodium citrate Na 3 C 6 H 5 O 7
• base metals such as copper and/or nickel may gradually build up in the solution. When this occurs it can slow down the rate of stripping and the iodine can be removed to form a new iodide-iodine stripping solution. This recovery and the reuse of elemental iodine results in an economical process.
• a potassium iodide-iodine solution for stripping gold is prepared by adding on a weight basis 1 part of iodine to 4 parts of potassium iodide to 10 parts of distilled water. Specifically, the potassium iodide is weighed out, added to the water and then stirred until dissolved. After the potassium iodide is dissolved, the weighed portion of iodine is added with stirring.
• the precipitated gold is removed by filtration and the I 3 - is regenerated to approximately its former strength by adding 5-6 ml of 30% hydrogen peroxide to every 100 ml. of stripping solution.
• the process overcomes many of the waste disposal and pollution abatement control problems of existing gold reclamation processes.
• a suitable vapor trap can be used to collect small amounts of iodine vapor which may escape from the solution during the process.
• the only other gases which are emitted by the process are non-polluting gases normally present in the air.
• the use of a buffer in the process minimizes salt buildup during the sequence of processing steps making it possible to repeat a larger number of closed loop cycles of usage.
• the process can also be used for the extraction of gold from gold bearing ores.
• the ore In processing gold bearing ore the ore is commonly ground, e.g., to approximately 200 mesh, and then treated.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Manufacture And Refinement Of Metals (AREA)
• ing And Chemical Polishing (AREA)

Priority Applications (2)

Applications Claiming Priority (1)

Publications (1)

Family

ID=23966003

Family Applications (1)

Country Status (2)

Cited By (39)

Families Citing this family (8)

Citations (4)

• 1974
  • 1974-08-05 US US05/494,794 patent/US3957505A/en not_active Expired - Lifetime
• 1975
  • 1975-08-05 JP JP50095320A patent/JPS5141625A/ja active Pending

Patent Citations (4)

Non-Patent Citations (2)

Also Published As

Similar Documents